1. Field of the Invention
The present invention relates to a torsion beam of a suspension of a vehicle, and more particularly, to a torsion beam of a suspension of a vehicle having a larger diameter of a rear tail than that of a front tail.
2. Description of the Background Art
As illustrated in FIG. 1, a suspension of a vehicle connects a vehicle body to wheels and absorbs shock and vibration applied from a road during traveling to improve a ride comfort and stability of the vehicle.
The suspension is categorized into an integrated type for connecting right and left wheels to each other by an axle and an independent type in which the right and left wheels are independently driven, and includes a spring 100 for absorbing shock transmitting from the road, a shock absorber 110 for improving a ride comfort by restricting free vibration of the spring 100, arms and links 120 for controlling operation of the wheels.
As a compromising type of the integrated type and the independent type, a torsion beam type suspension includes left and right trailing arms 120 that are coupled with each other by a single member called as a cross beam or a torsion beam 130. The torsion beam suspension is characterized in that a length of the link is short in comparison to a strut type and a double wishbone type, the number of rubber bushes serving as a vibration shaft is little, friction hysteresis is less during the suspension stroke, and high end ride comfort is enabled.
Moreover, although designed performance region is not high due to simple components, the torsion beam suspension has been with low cost used in rear wheel suspensions of a subcompact car and a premium mid-size car for scores of years due to a relatively high traveling stability in comparison to low manufacturing cost and light weight.
FIG. 2 is a perspective view illustrating a conventional suspension of a vehicle, and FIGS. 3A to 3D and 4 are sectional view illustrating respective parts of the conventional suspension.
A torsion beam 130 of the conventional suspension of a vehicle plays an important part of controlling roll stiffness, lateral stiffness, and toe variation, and a tubular beam type torsion beam in which a reinforced plate and a torsion bar are not required, the number of components can be reduced, and weight can be reduced, is widely used.
Hereinafter, the tubular beam type torsion beam will be described in detail as follows.
The tubular beam type is manufactured in such a way that a pipe-shaped member is positioned between upper and lower presses in which one of the presses moved up and down, to press the pipe-shaped member.
The conventional tubular beam type manufactured as described above, as illustrated in FIGS. 3A to 3D, is broadened from the middle portion of the torsion beam 130 to right and left ends of the torsion beam 130 in the longitudinal direction of the torsion beam 130, that is, as goes toward the place where the trailing arms 120 is disposed.
Moreover, as illustrated in FIG. 4 which is a sectional view taken along the line E-E of FIG. 2, lateral sections of the right- and left portions positioned symmetric with respect to the middle portion of the torsion bean 130 has an upper line 132 which is approximately horizontal and a lower line 134 comprising the first linear part 134A, the second linear part 134B, and the third linear part 134C.
The first linear part 134A of the lower line 134 extends horizontally from the middle portion to its distal end portion in the longitudinal direction of the torsion beam 130. The second linear part 134B of the lower line 134 extends downwardly inclined from the distal end portion of first linear part 134A. The third linear part 134C of the lower line 134 extends horizontally from the distal end portion of the second linear part 134B to the distal end portions of the torsion beam 130 in the longitudinal direction of the torsion beam 130.
Furthermore, the tubular type beam torsion beam 130 has a structure symmetrical with respect to the middle portion of the front-to-rear direction of the vehicle.
However, the conventional tubular type torsion beam has the following drawbacks.
Firstly, in FIG. 3A which is a sectional view taken along the line A-A of FIG. 2, a rolling force is assumed to be applied to a portion of the torsion beam 130 for an explanation.
In the drawing, a dotted arrow A1 indicates a sheer flow resisting the rolling force applied to the torsion beam 130. The solid arrow B1 indicates a reactive force generated by a bending moment caused by the rolling force.
In the tubular beam type torsion beam 130, as illustrated in FIG. 3A, the shear flow A1 resisting the rolling force and the reactive force B1 generated by the bending moment may be canceled at the rear tail T2 because of their opposite action directions each other. In contrast, at the front tail T1, the direction of the shear flow A1 resisting the rolling force and the direction of the reactive force B1 generated by the bending moment are in the same direction so that the resultant reactive force at the front tail T1 is not canceled but increased.
Meanwhile, in the conventional scheme, the sizes of the front and rear tails T1 and T2 are decreased to increase the shear flow A1 resisting the rolling force. However, in this case, the increased shear flow deteriorates the durability of the torsion beam 130 since the concentration of stress is increased.
Moreover, as illustrated in FIG. 4, shear stress is easily concentrated at the connection portion between the first and second linear parts 134A and 134B of the lower line 134 of the torsion beam 130 due to the abrupt change of the slope between the first and second linear parts 134A and 134B.
Further shear stress is easily concentrated at the connection portion between the second and third linear parts 134B and 134C of the lower line 134 of the torsion beam 130 due to the abrupt change of the slope between the second and third linear parts 134B and 134C.
These concentrated shear stresses make cracks occur at the connection portions easily. In other words, as indicated by Arabian numbers in FIGS. 5A to 5C, the roll stiffness and the durability are inferior due to the rolling and the spring reactive force.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.